Mobile aerial tower structure



Feb. 16, 1965 L. L. MYERS 3,169,602

MOBILE AERIAL TOWER STRUCTURE ATTORNEYS Feb. 16, 1965 1.. MYERS 3,169,602

MOBILE AERIAL TOWER STRUCTURE Filed June 7, 1962 2 Sheets-Sheet 2 2;; iii 2:; ii 5;; 5*?

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LESTER L. MYERS BY X40112, fiwwhw ATTORNEYS United States Patent M 3,169,662 MOBILE AERIAL TGWER STRUCTURE Lester L. Myers, Fort Wayne, Ind, assignor to Mobile Aerial Towers, Inc, Fort Wayne, Ind. Filed June 7, 1962, Ser. No. 200,875 3 Claims. ((11. 18246) The present invention relates to a mobile aerial tower structure and more particularly to structure for elevating personnel into close proximity to electrical power lines which are in the process of being either constructed or maintained.

Mobile aerial towers of the so-called cherry picker type conventionally comprise a mobile platform or truck upon which a tower structure is mounted for three-dimen sional operation. The tower structure conventionally includes a pedestal mounted on the truck having a rotatable platform on the upper end thereof. An elongated lower boom is pivotally mounted on the rotatable platform at one end for swinging movement about a horizontal axis. To the other end of the lower boom is pivotally connected an upper boom for swinging movement about a horizontal axis. To the remaining, outer end of the upper boom is pivotally connected a personnel bucket which is at all times maintained in a level position regardless of the position and elevation to which the two booms may be moved. Suitable motors are connected to the rotatable platform and to the booms, respectively, by which rotary motion of the booms may be obtained as well as relative swinging movement thereof, such booms being swingable to a lower position in which the personnel bucket is adjacent to the truck and to an elevated position of a desired height above the truck within the limits of the boom dimensions.

Such towers are conventionally used in the construction or maintenance of electrical power lines, and it is quite common for workmen to operate on the power lines while the latter are elevated and carrying relatively high voltages. For this purpose, it is essential in the first instance that the personnel bucket be adequately strong to support the weight of a workman as well as the equipment which he must use while in an elevated position. Also, it is necessary that the bucket in and of itself be relatively light in weight to reduce the load placed on the articulated booms to a minimum. Additionally, the bucket should be of high dielectric strength in order to protect a man from danger in the event he should come into contact with a charged power line. Still further, it is necessary that the bucket structure be impervious to moisture so as to maintain the dielectric strength thereof in order to prevent the conduction of electrical currents from the power lines to the workman in the event the bucket should either come in contact with or approach closely a power line.

Such personnel buckets are conventionally fabricated of resin or plastic which is reinforced with glass thread or fiber. Such reinforced plastic has considerable strength to weight ratio; however, in order to provide adequate dielectric strength for the purpose of working on power lines, it is necessary that the wall thickness of this reinforced plastic be substantial. The resultant structure, in this instance, is so heavy that its utility for the intended purpose becomes impaired such that other means must be resorted to for providing the dielectric strength.

Prior to the time of this invention, in providing a bucket arrangement which was of lightweight, strong construction and yet provides the necessary dielectric strength, the bucket itself was fabricated of relatively thin but rigid plastic reinforced with glass fibers and used as the main personnel supporting structure and a bucket-shaped polyethylene liner was removably inserted thereinto. The resultant assembly provided the 3,169,632 Patented Feb. 16, 1965 requisite dielectric strength while retaining the necessary characteristics of being relatively light in weight but nevertheless strong as a supporting structure. However, the use of such a polyethylene liner is not entirely satisfactory inasmuch as the liner itself is relatively heavy, it must be easily removable from the outer shell, and furthermore must be removed and periodically tested for dielectric strength. As one of the desirable features of this prior art assembly, it is contended that if the liner should be filled or even partially filled with water as the result of rainy weather, it is only necessary to remove manually the liner from the outer shell and pour out the water instead of alternatively dipping and swabbing out such water. However, this has proven not to be an advantage with respect to this particular arrangement inasmuch as the liner in the first instance is quite heavy such that when even a small quantity of water is contained therein the weight is so heavy that the water must be dipped out to a relatively low level before the liner can be removed manually. In the usually instance, it has been found to be more convenient to merely dip out the water and otherwise dry out the bottom of the liner by swabbing with a rag or sponge.

Also, it has been found necessary in the use of the removable liner to remove it and test it periodically for dielectric strength. If apparatus is not conveniently available to the operator of the tower for such testing purposes, this usually requires that the liner to be sent to a factory or the like where such testing can be performed. Alternatively to this, an extra liner may be purchased and kept available, which adds to the expense and complicates storage and handling of this extra equipment.

In view of these disadvantages of the prior art arrangements, it becomes desirable to provide a bucket construction having the requisite characteristics of permanency, physical strength, lightweight, high dielectric strength, and moisture impermeability. Additionally, it is desirable that the bucket be so constructed that periodic testing of the dielectric strength is not necessary. In view of these desirable design features it is an object of this invention to provide a personnel bucket having these characteristics.

It is another object of this invention to provide a permanent, integral personnel bucket construction for a mobile aerial tower which is impervious to moisture, light in weight, physically strong, and having high dielectric strength.

Other objects will become apparent as the description proceeds.

The above-mentioned and other features and objects of this invention and the manner of attaining them will become more apparent and the invention itself will be best understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a side elevation of one embodiment of the present invention;

FIG. 2 is a side elevation of an embodiment of the personnel bucket;

FIG. 3 is a top plan view of the bucket of FIG. 2;

FIG. 4 is an end view, partially sectioned, of the bucket of FIG. 2;

FIG. 5 is a longitudinal sectional illustration taken substantially along section line 5-5 of FIG. 2;

FIG. 6 is an enlarged fragmentary section showing the perimetral cap of the bucket of the preceding figures; and

FIG. 7 is a fragmentary cross-sectional illustration taken substantially along section line 77 of FIG. 4.

Referring to the drawings, and more particularly to FIG. 1, a truck 10 is shown as having a supporting as will appear from the following description.

pedestal 12 mounted on the bed thereof which carries a platform 14 for rotation about a vertical axis. Pivotally mounted on the platform 14 is an elongated, lower boom 16, the pivotal connection between the platform 14 and boom 16 being provided by a horizontally extending pin or shaft 18. A power cylinder 29 has one end pivotally connected to the boom 16 at 22 and the other end pivotally connected to the platform 14 at 24. By operation of this power cylinder 20, the boom 16 may be raised to the illustrated full-line position or depressed to the dashed-line position. The power cylinder 29 can move and hold the boom 16 to any intermediate position.

Pivotally connected to the outermost end of the lower boom 16 is an elongated upper boom 26, the pivotal connection between these two booms being provided by means of a suitable pin or shaft 28 passing through the respective ends of these booms. This pin or shaft 23 has its axis arranged horizontally such that the two booms 16 and 26 may be relatively moved in a common vertical plane.

On the distal end of the upper boom 26 is pivotally mounted a personnel bucket 3% in which a workman, as shown, may ride and control his spatial position. By means of suitable controls mounted either in or on the bucket 39, the rotational position of the platform 14, hence the rotational position of the bucket 30, may be controlled. Also, the pivoted position of the lower boom 16 may be controlled with respect to the platform 14. Additionally, the pivotal relationship between the lower and upper booms 16 and 26, respectively, may be controlled. The operator or workman can thereby move himself to any spatial position within the dimensional limits afforded by the tower.

The particular construction of the personnel bucket 33 is shown in its various details in FIGS. 2-7 inclusive. It is of rectangular cross-section in the illustrated embodiment; however, it may take other and different shapes The bucket structure comprises essentially three laminations 32, 34 and 36, each of these laminations conforming to the final shape of the bucket and providing a relatively flat bottom and four sides upstanding therefrom. The laminations are integrated into a permanent structure in which a workman may ride, which is physically strong and relatively light in weight. Furthermore, it is substantially impervious to moisture and provides a relatively high dielectric strength as will appear from the description to follow.

The two laminations 32 and 36 are fabricated of plastic material, such as epoxy or polyester resin, reinforced with glass or other suitable fiber. The particular composition of these laminations is conventional, such composition being commonly used in the fabrication of so-called glass boats. As reinforcement, both glass roving and woven cloth may be used.

These laminations 32 and 36 are formed with bottoms and sides upstanding therefrom, these bottoms and sides being parallel and uniformly spaced apart as shown. The bottoms are preferably flat as shown. The upper edges 38 and 40 of these two laminations 32 and 36 respectively preferably terminate in a common plane, a flange 42 extending laterally outwardly from one edge 33 along one lateral side of the bucket as shown.

Also, the outer lamination 32 is provided with two upright, spaced-apart and parallel, molded ribs .4 and 46, these two ribs being substantially identical in construction. These ribs extend from near the top of the bucket to near the bottom thereof as shown and are relatively thin. Extending into and being intimately molded as a part thereof is a fiat, elongated supporting plate 48 having a portion 5b projecting outwardly thereof. A wooden filler member 5'2 also extending internally of each rib 4-4, 46 for substantially the entire length thereof provides reinforcement and additional strength for the molded fiberglass portions of the two ribs 44 and 46.

4- A suitable mounting bar 54 connects at its opposite ends to the two supporting plates 48 and provides a means by which the bucket 39 may be attached pivotally to the outermost end of the upper boom 25.

Referring more specifically to FIG. 5, it will be noted that the two laminations 32 and 36 are spaced relatively far apart. This space is completely filled with a suitable lightweight cellular plastic, polyurethane foam as an example, being found to be particularly well adapted to the present invention. This polyurethane foam after hardening provides a relatively stiff and thick middle lamination 56 which tenaciously adheres to the facing walls of the two laminations 32 and 35. It should be stated at this point that it is especially desirable to have these facing surfaces of the laminations 32 and 36 finished rough with many depressions and raised portions for providing a relatively large amount of surface area to which the foam center 56 can bond. As a consequence of this structure, the bucket is stiff and rigid and quite strong in comparison with the weight thereof.

Again as shown more clearly in FIG. 5, the bottoms 58 and of the two laminations 32 and as are flat, spaced-apart and parallel. in order to provide strength in the corners where the lamination sides and bottoms join, the corners are rounded or radiused as shown. The outer lamination 32 has the side and bottom 5:; joining in a corner 62. of relatively large radius by which maximum strength can be obtained. The corners 64 at which the sides and bottom 6% of the inner lamination 36 join are also rounded with the radius thereof being much smaller than that for the outer corner 62. By making the radius of these corners 6d quite small, it is possible for the bottom 69 of the inner lamination 36 to constitute the floor of the bucket on which the workman can stand. In conventional constructions, the bucket is provided with such a large radius at the corners 64, or what would be regarded as the equivalent of these corners 64, that it is necessary to provide a false floor structure which extends outwardly laterally against the inner side of the bucket such that the workmans toes can reach the bucket side. When the corners 64 are relatively large in radius, such radius prevents the workman from comfortably working from the bucket with his toes adjacent to the bucket side. In the present invention, since two laminations 32 and 36 are provided,

only the corners 62 need to be of fairly large diameter.

The center or foam lamination 56 may be fabricated in the usual way by pouring the necessary chemical constituents into the space between the laminations 32 and 3t: and allowing the chemical reaction to take place which results in the formation of a foam which completely fills and exudes from between the upper edges 35: and 40 of the two laminations. While the foam is yet uncured and just before complete solidification, the upper edge of the foam may be stricken ofi flush with the upper edges 38 and 46. In the alternative, if the foam should harden before being stricken off, it can easily be sawed or cut 013 flush with the upper edges 33 and 49.

Before pouring the chemical constituents for producing the foam in the space between the two laminations 32 and 36, the latter are fitted with suitable molds which intimately engage the sides and bottoms thereof. For example, the lamination 32 is first inserted into a female mold having the exact shape of the outer bucket surface. Similarly, a male mold having the exact inner shape and size of the finished bucket is inserted into the lamination 36. Means are provided for spacing the two laminations apart uniformly around the sides and bottoms thereof while the foam chemicals are being introduced into the space between the two laminations 32 and 3d. As the foamin takes place, the considerable lateral force exerted thereby will be resisted by the two molds thereby preventing the laminations 32 and 36 from becoming distended. By this means, the sides of the bucket may be kept straight and uniform until the foam takes a permanent set. Following this, the molds are removed.

As a final step in the fabrication of the bucket, a

perimetral cap formed of either the same materials as the.

laminations 32 and 36 or of a suitable rubber-like material is fitted over the upper perimetral edge as shown. This cap indicated by the numeral 65 has depending sides which intimately engage and extend downwardly over the opposite outer surfaces of the two laminations 32 and 36, and in order to prevent moisture from leawg upwardly and into the space over the exposed edges of the three laminations, a suitable adhesive which may be either a polyester or epoxy resin may be used for sealing the cap sides to the surfaces of the two laminations 32 and 36. As shown more clearly in FIG. 5, the cap is made sufiiciently large in transverse dimension to extend from the inner surface of the lamination 36 to the outermost edge of the flange 42 and the ribs 46.

As clearly shown in FIG. 5, the foam plastic lamination 56 is many times thicker than the two laminations 32 and 36. In a practical embodiment of this invention,

,the thickness of the foam plastic lamination 55 may be'two (2) inches while the thickness of each of the laminations 32 and as may be one-eighth /8) inch each. For a bucket height of forty-four (44) inches, the laminations 32 and 315 per .se are flexible; however, with the foam plastic lamination 56 in place, the resulting structure is quite rigid, stiff and strong. Also, in this practical embodiment, the radii of the corners 62 and 64 are 2% inches and one-half /2) inch, respectively.

The thicker the lamination 56, the greater is the dielectric strength of the finished bucket. For work on exceptionally high voltage power lines, the foam plastic lamination 56 should be quite thick. For correspondingly 'lower voltages, the lamination 56 does not need to be so thick. However, the bucket preferably is initially constructed with adequate thickness to operate even on the highest voltage power lines wmch may be serviced while hot inasmuch as the weight and density of the foam plastic 56 are so small that relatively thick dimensions therefore produce very little additional weight in the entire bucket assembly. Thus, a satisfactorily high dielectric strength may be initially designed into the bucket such that it may be used in almost any desired work on power lines.

Inasmuch as the plastic lamination 5'6 is impervious to moisture and also tenaciously adheres to the laminations 32 and 36, no moisture can penetrate the thickness of the bucket wall. Thus, insofar as moisture is concerned, the dielectric strength of the bucket remains substantially constant with time. Also, by reason of the substantial thickness in the foam lamination 56, a substantial spacing is alway maintained between any power line which may touch the outer lamination 32 and the workman riding inside the bucket. This relatively great physical spacing is ideal inasmuch as the fiberglass laminations 32 and 35 characteristically develop cracks and the like after a period of usage through which a conductive path is formed. However, since the foam plastic layer 51? provides the major part of the dielectric strength in the bucket structure, any voids, air bubbles, interstices or cracks in the glass fiber laminations 32 and 36 will not render use of the bucket dangerous.

Since the dielectric strength of the bucket remains substantially high and constant throughout the normal life thereof, it is obvious that periodic testing for dielectric strength is not necessary. This is particularly advantageous inasmuch as the mobile aerial tower on which the bucket is used never has to be placed out of service for a period of time necessary within which to test the bucket dielectricity.

Also in contrast with prior art buckets, the bucket of this invention can tolerate small punctures or holes without any danger to the operator. For example, if the lamination 32 should be punctured, the dielectric strength of the bucket wall will be, at the most, only negligibly impaired whereupon minor damage to the bucket can ordinarily be ignored.

While I have described above the principles of my invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of my invention.

What is claimed is:

1. The combination of apparatus for elevating a workman to selected heights for working in the vicinity of electrical power lines comprising a vehicle, a turntable mounted on said vehicle for rotation about an upright axis, a lower boom pivotally mounted at one end on said turntable for swinging movement about a horizontal axis, an upper boom pivotally connected at one end to the other end of said lower boom for swinging movement about a horizontal axis, a personnel bucket having a bot tom and sides upstanding therefrom and mounted on the other end of said upper boom; said bucket being of integral construction and including an inner lamination of glass fiber reinforced plastic, said plastic being one of the group of polyester and epoxy, an outer lamination of glass fiber reinforced plastic extending parallel to and spaced from said inner lamination, the last-mentioned plastic being one of the group of polyester and epoxy, both said laminations having upper edge portions lying in a common plane, said laminations having upstanding sides and bottom portions respectively, the facing surfaces of said laminations being irregular and rough, a middle lamination of polyurethane foam filling the space between said inner and outer laminations and being rigidly adhered said facing surfaces, said foam lamination being stiff and substantially thicker than said inner and outer laminations by an amount to physically space the latter apart to provide a predetermined dielectric strength and to render the bucket rigid and relatively inflexible, a perimetral cap of channel-shaped cross-section fitted over the upper composite edge of said laminations, said cap having opposite side portions which engage and extend down wardly over the opposite outside surfaces of said inner and outer iaminations respectively, said cap being adhered to and sealed to said laminations by means of an adhesive thereby preventing moisture from entering between said inner and outer laminations; and means for attaching said other end of said upper boom to said outer lamination.

2. The apparatus of claim 1 wherein the outer lamination has an integral elongated glass fiber reinforced plastic rib extending outwardly from one side thereof in a direction between said bottom and said upper edge, said rib having an elongated flat metal mounting plate embedded therein in parallelism therewith with one portion of said plate extending outwardly beyond said rib for attachment to said upper boom, and a wood filler member inside said n'b andextending the full length thereof, said filler member being intimately engaged with said rib for reinforcing the same.

3. in combination, a personnel bucket of integral construction for supporting a workman in an elevated position on the boom of a mobile aerial tower for working in the vicinity of high voltage electrical power lines, comprising an inner lamination of glass fiber reinforced plastic, an outer lamination of glass fiber reinforced plastic extending substantially parallel to and spaced from said inner lamination, said laminations having substantially flat bottoms and sides upstanding therefrom respectively, a core lamination of cellular plastic material, said plastic material being an electrical insulator, said core lamination filling the entire space between said inner and outer laminations and being rigidly adhered thereto, the combination of said inner, outer and core laminations providing an integrated, rigid and physically strong structure in which a workman may ride, said core lamination being thicker than said inner and outer laminations by an amount to provide for a predetermined dielectric strength and for maintaining a minimum spacing between said laminations and between a workman in said bucket structure and an electrical line touching the outer surface of said outer lamination, and means for mounting said outer lamination on the end of a boom.

4. In combination, a personnel bucket of integral construction for supporting a workman in an elevated position on the boom of a mobile aerial tower for working in the vicinity of high voltage electrical power lines, comprising an inner lamination of glass fiber reinforced plastic, an outer lamination of glass fiber reinforced plastic extending substantially parallel to and spaced from said inner lamination, said laminations having substantially flat bottoms and sides upstanding therefrom respectively, a core lamination of cellular plastic material, said plastic material being an electrical insulator, said core lamination filling the entire space between said inner and outer laminations and being rigidly adhered thereto, the combination of said inner, outer and core laminations providing an integrated, rigid and physically strong structure in which a Workman may ride, said core lamination being thicker than said inner and outer larninations by an amount to provide for a predetermined dielectric strength and for maintaining a miniumum spacing between said laminations and between a workman in said bucket structure and an electrical line touching the outer surface of said outer lamination, one side of said outer lamination having two spaced apart upright portions; an elongated boom member having opposite ends, and means connecting said upright portions to one end of said boom for mounting said bucket structure on said boom.

5. In combination, a personnel bucket of integral construction for supporting a workman in an elevatedposition on the boom of a mobile aerial tower for working in the vicinity of high voltage electrical power lines, comprising an inner lamination of glass fiber reinforced plastic, an outer lamination of glass 1 her reinforced plastic extending substantially parallel to and spaced from said inner lamination, said plastics being one of the group of epoxy and polyester, said laminations having substan- -tially fiat bottoms and sides upstanding therefrom respectively, a core lamination of cellular plastic material, said plastic material being an electrical insulator, said core lamination filling the entire space between said inner and outer laminations and being rigidly adh red thereto, the combination of said inner, outer and core laminations providing an integrated, rigid and physically strong structure in which a workman may ride, said core lamination being thicker than said inner and outer laminations by an amount to provide for a predetermined dielectric strength and for maintaining a minimum spacing between said laminations and between a workman in said bucket structure and an electrical line touching the outer surface of said outer lamination; a tower boom having opposite ends and means including said outer lamination for pivotally mounting said bucket on one end of said boom.

a 3 6. In combination, a personnel bucket of integral construction for supporting a workman in an elevated position on the boom of a mobile aerial tower for Working in the vicinity of high voltage electrical power lines,

comprising an inner lamination of glass fiber reinforced plastic, an outer lamination of glass fiber reinforced plastic extending substantially parallel to and spaced from said inner lamination, said laminations having substantially flat bottoms and sides upstanding therefrom respectively, a core lamination or" cellular plastic material, said plastic material being an electrical insulator, said core lamination filling the entire space between said inner and outer laminations and being rigidly adhered thereto, the combination of said inner, outer and core laminations providing an integrated, rigid and physically strong structure in which a workman may ride, said core lamination being thicker than said inner and outer laminations by an amount to provide for a predetermined dielectric strength and for maintaining a minimum spacing between said laminations and between a workman in said bucket structure and an electrical line touching the outer surface of said outer lamination, two mounting portions on one side of said bucket structure spaced apart in a direction parallel to said bottom, said two mounting portions including two separated portions of said outer lamination, and means extending etween and connected to said two mounting portions for mounting said bucket structure on one end of a boom.

7. The combination of claim 6 wherein said two mounting portions are flat and lie in planes extending transversely to said one side, and said means is a bar member connected at its opposite ends to said two mounting portions, respectively.

8. The combination of claim 6 having two supporting plates secured to and flush with the aforesaid two separated portions respectively of said outer lamination, said means including a member having two opposite end portions secured to said two plates, respectively, whereby 'said bucket structure may be mounted on one end of HARRISON R. MOSELEY, Primary Examiner.

FRANK B. SHERRY, REINALDO l. MACHADO,

Examiners. 

3. IN COMBINATION, A PERSONNEL BUCKET OF INTEGRAL CONSTRUCTION FOR SUPPORTING A WORKMAN IN AN ELEVATED POSITION ON THE BOOM OF A MOBILE AERIAL TOWER FOR WORKING IN THE VICINITY OF HIGH VOLTAGE ELECTRICAL POWER LINES, COMPRISING AN INNER LAMINATION OF GLASS FIBER REINFORCED PLASTIC, AND OUTER LAMINATION OF GLASS FIBER REINFORCED PLASTIC EXTENDING SUBSTANTIALLY PARALLEL TO AND SPACED FROM SAID INNER LAMINATION, SAID LAMINATIONS HAVING SUBSTANTIALLY FLAT BOTTOMS AND SIDES UPSTANDING THEREFROM RESPECTIVELY, A CORE LAMINATION OF CELLULAR PLASTIC MATERIAL, SAID PLASTIC MATERIAL BEING AN ELECTRICAL INSULATOR, SAID CORE LAMINATION FILLING THE ENTIRE SPACE BETWEEN SAID INNER AND OUTER LAMINATIONS AND BEING RIGIDLY ADHERED THERETO, THE COMBINATION OF SAID INNER, OUTER AND CORE LAMINATIONS PROVIDING AN INTEGRATED, RIGID AND PHYSICALLY STRONG STRUCTURE IN WHICH A WORKMAN MAY RIDE, SAID CORE LAMINATION BEING THICKER THAN SAID INNER AND OUTER LAMINATIONS BY AN AMOUNT TO PROVIDE FOR A PREDETERMINED DIELECTRIC STRENGTH AND FOR MAINTAINING A MINIMUM SPACING BETWEEN SAID LAMINATIONS AND BETWEEN A WORKMAN IN SAID BUCKET STRUCTURE AND AN ELECTRIC LINE TOUCHING THE OUTER SURFACE OF SAID OUTER LAMINATION, AND MEANS FOR MOUNTING SAID OUTER LAMINATION ON THE END OF A BOOM. 